I don't know The answer to life, the universe, and everything.
But I know this is NOT a completed kata, please correct the test mothods and add random tests ;-)

Also, one of your test case is wrong:

Test.assertEquals(groupClouds([[ true,false, true],[false, true,false,false, true]]), 3, "Assumes null outside grid/array are false");

The array is

[ [ true, false, true, false, false ],
  [ false, true, false, false, true ] ]

As you can see, there are only 2 groups (((0,0),(1,1),(2,0)) and (4,1)).

Please solve your own kata properly :P

See my second solution.